オブジェクトのリストを Excel に簡単にエクスポートできるように、jExcelApi クラスのラッパーを作成しました。オブジェクトの作成を最小限に抑えるために、セル形式は静的フィールドとして作成され、エクスポートの連続呼び出しで再利用されます。しかし、日付形式に問題があります-最初の呼び出しはうまく機能しますが、連続したすべてのエクスポートで、日付セルには日付形式ではなく数値形式があります。静的フィールドを使用する代わりに日付形式の新しいオブジェクトを作成すると、すべて問題ありません。異なるシートまたはワークブックに同じフォーマット オブジェクトを使用すると失敗する理由はありますか?
例外処理を簡素化し、他のデータ型を省略し、おそらくいくつかのインポートが欠落しているコードを次に示します。
ExcelCellGenerator.java:
import jxl.write.WritableCell;
public interface ExcelCellGenerator<T> {
WritableCell getCell(int col, int row, T arg);
}
ExcelCellGeneratorFactory.java:
import jxl.write.DateFormat;
import jxl.write.DateTime;
import jxl.write.Label;
import jxl.write.NumberFormat;
import jxl.write.NumberFormats;
import jxl.write.WritableCell;
import jxl.write.WritableCellFormat;
import ExcelExporter.DateTimeExtractor;
final class ExcelCellGeneratorFactory {
private ExcelCellGeneratorFactory() {}
private static final WritableCellFormat DATE_FORMAT = new WritableCellFormat ( new DateFormat ("dd MMM yyyy hh:mm:ss")); // reusing this field fails
static public <T> ExcelCellGenerator<T> createDateCellGenerator(final DateTimeExtractor<T> extractor) {
return new ExcelCellGenerator<T>() {
public WritableCell getCell(int col, int row, T arg) {
return new DateTime(col, row, extractor.extract(arg), DATE_FORMAT);
// if there is new WritableCellFormat(new DateFormat(...)) instead of DATE_FORMAT, works fine
}
};
}
}
ExcelExporter.java:
import jxl.Workbook;
import jxl.write.DateFormat;
import jxl.write.DateTime;
import jxl.write.Label;
import jxl.write.NumberFormat;
import jxl.write.WritableCellFormat;
import jxl.write.WritableSheet;
import jxl.write.WritableWorkbook;
public class ExcelExporter<T> {
// describe a column in Excel sheet
private static class ColumnDescription<T> {
public ColumnDescription() {}
// column title
private String title;
// a way to generate a value given an object to export
private ExcelCellGenerator<T> generator;
}
// all columns for current sheet
private List<ColumnDescription<T>> columnDescList = new ArrayList<ColumnDescription<T>>();
// export given list to Excel (after configuring exporter using addColumn function
// in row number rowStart starting with column colStart there will be column titles
// and below, in each row, extracted values from each rowList element
public byte[] exportList(int rowStart, int colStart, List<? extends T> rowList) {
final ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
WritableWorkbook workbook;
try {
workbook = Workbook.createWorkbook(outputStream);
} catch (IOException e) {
e.printStackTrace();
}
final WritableSheet sheet = workbook.createSheet("Arkusz1", 0);
int currRow = rowStart;
try {
int currCol = colStart;
for (ColumnDescription<T> columnDesc : columnDescList) {
final Label label = new Label(currCol, currRow, columnDesc.title);
sheet.addCell(label);
currCol++;
}
currRow++;
for (T object : rowList) {
currCol = colStart;
for (ColumnDescription<T> columnDesc : columnDescList) {
sheet.addCell(columnDesc.generator.getCell(currCol, currRow, object));
currCol++;
}
currRow++;
}
workbook.write();
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
workbook.close();
} catch (Exception e) {
e.printStackTrace();
}
}
return outputStream.toByteArray();
}
// configure a Date column
public ExcelExporter<T> addColumn(String title, DateTimeExtractor<T> extractor) {
final ColumnDescription<T> desc = new ColumnDescription<T>();
desc.title = title;
desc.generator = ExcelCellGeneratorFactory.createDateCellGenerator(extractor);
columnDescList.add(desc);
return this;
}
// and test that shows the problem
public static void main(String []args) {
final ExcelExporter<Date> exporter = new ExcelExporter<Date>();
exporter.addColumn("Data", new DateTimeExtractor<Date>() {
public Date extract(Date date) {
return date;
}});
// this file looks OK
FileOutputStream ostream = new FileOutputStream("C:\\tmp\\test1.xls");
try {
ostream.write(exporter.exportList(0, 0, Collections.singletonList(new Date())));
} finally {
ostream.close();
}
// but in this file date is shown in cell with numeric format
final ExcelExporter<Date> exporter2 = new ExcelExporter<Date>();
exporter2.addColumn("Data", new DateTimeExtractor<Date>() {
public Date extract(Date date) {
return date;
}});
ostream = new FileOutputStream("C:\\tmp\\test2.xls");
try {
ostream.write(exporter2.exportList(0, 0, Collections.singletonList(new Date())));
} finally {
ostream.close();
}
}
}